364 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



pose. One should consult some of the Government or Experi- 

 ment Station Bulletins (see page 419) for directions for making 

 and using these. 



Similar diseases caused by other species of the genus Babesia 

 occur in horses, sheep, dogs and other animals, but none is so 

 important as the Texas fever of cattle. 



OTHER PROTOZOAN DISEASES 



Spotted Fever. Spotted fever, or Rocky Mountain fever, 

 is a disease that occurs in the mountains in the northwestern 

 United States. It is transmitted by ticks, Dermacentor ven- 

 ustus, and is supposed by many to be due to an organism closely 

 related to, or belonging to the genus Babesia. It has been 

 shown that domestic animals, particularly the larger ones, 

 in the region where the fever occurs, are the principal hosts 

 for the adult ticks, so if these animals can be kept free from 

 ticks, by dipping and otherwise, the disease can be largely 

 controlled. 



Pebrine of Silkworms. About the middle of the nine- 

 teenth century a strange malady appeared among the silk- 

 worms in Southern France and caused enormous losses. The 

 silk growers knew nothing of the nature of the disease, and were 

 at a loss to know how it spread, for even though they placed 

 the eggs of the silk-worm moth in perfectly clean places and 

 took the very best care of the larvae, the silk-worms would 

 suddenly sicken and die at a certain stage of their development. 

 Pasteur, who was then just beginning his great work, made a 

 careful study of the disease and discovered that it was caused 

 by a sporozoan. It was found that this parasite, now known 

 as Glugea (Nosema) bombycis, was so minute that it would 

 enter the eggs before they were laid by the moth, so that the 

 larvae were affected from the time they hatched, although the 

 disease did not manifest itself until a later stage in their devel- 

 opment. The disease is known as pebrine, and was the first 

 disease proved to be due to an infection by a Protozoan 

 parasite. In several countries where silk-worm growing is 

 an important industry, Government experts now examine all 

 the eggs that are used for hatching and only those that, by 



